This is just the start for 'Obama's War' in Afghanistan

In the thick of it: US Marines in a firefight with Taliban in Marjah, Helmand

Make no mistake: we may have become used to images of British troops in action in Afghanistan but this latest offensive is a "must-win" campaign for the Coalition.

They hope it will turn a psychological corner in convincing the Afghan people, the Taliban and their part-time supporters that the Coalition and the Karzai government will be the eventual winners. And for the next 12 months, it matters most in Helmand and Kandahar. This is where the psychological battle will be won and lost — among the two million people under the Coalition's security blanket.

That is why it would be a mistake to judge the success of troops in Operation Moshtarak only by military measures. Yes, the military will take the ground. Yes, they will hold on to it. The forces deployed are sufficiently strong, the planning and technology sufficiently good and it has never been hard to clear the Taliban out of an area. The problem has always been stopping them from coming back. This is the yardstick by which the immediate success of Operation Moshtarak will be judged.

It will not be straightforward. Many of those disgruntled locals who fight with, but not for, the Taliban have hidden their weapons and resumed their day jobs as farmers, traders, even policemen. Keeping the trained Taliban fighters out of the cleared area also involves keeping part-time local Taliban who remain inside the area in a state of quiescence.

Nevertheless, the military is capable of achieving all this, even though there will undoubtedly be sniping, explosions and some unpleasant scenes after the first impetus of the advance. Phase one of any military operation tends to go the way it was planned; phase two rarely does.

The campaign is well co-ordinated. The arrival of more American troops and the beefing-up of existing Nato forces means there are now, at last, enough boots on the ground. The challenges will come in the later "hold and build" stages. Much less air power is being used by the Coalition, to minimise the risks of civilian casualties. But there have already been two civilian tragedies and there may be more.

Most importantly, the operation is intended as a civil/military campaign that will immediately bring trained Afghan administrators into central Helmand, a new cadre of Afghan police, development money and very competent Afghan Army units to build security on the back of what Coalition forces have created. All this is part of the campaign plan. It is classic counter-insurgency strategy — and at long last it is being put into practice with the resources to make it work.

But true judgment on the operation's success will revolve around other questions. Afghan administrators and special police have been trained for just this mission. But how good will they be after six months or more in a part of Afghanistan they have not lived in for a long time — or ever? It will be a real test of local politics to channel development money effectively through a new group of Afghan administrators who will still have to work with the tribal and family structures that were there already.

How expensive will the operation turn out to be in civilian casualties? Just one incident a week will undermine all the gradual trust Coalition forces and their Afghan colleagues are trying to build up in territories that were formerly controlled by the Taliban.

Another test will revolve around what the Taliban do next. If most have moved out of the area, where will they regroup? Will their commanders in Pakistan try to stretch the Coalition forces in a new direction? The reported capture there today of top commander Mullah Abdul Ghani Baradar is significant but the Taliban are fluid and informal in nature. It is possible that they will simply disperse and mount ineffective attacks. But the Taliban are good at spotting new Coalition weaknesses and bringing their fighters to bear on it. If they can, they will try to provoke the Coalition into causing many more civilian deaths.

Not least, the operation has to appeal to people in Kabul and Jalalabad as much as it does to those in London, Washington or Paris. It is only possible to have one strategic message at a time. Western leaders have tried to have different messages for different audiences and the result has been a disaster.

This time they have to maintain their clarity, and their nerve, when casualties begin to mount; to make the world believe the military campaign can become progressively "Afghanised" without becoming ineffective. They have to stop talking about withdrawal timetables and concentrate on the "prevail or fail" choice they really now face.

This will be harder for some politicians than others. For President Obama, the immediate priority is to get through the mid-term elections in November with a sense of progress. He has an immoveable meeting with the electorate in 2012 and he will have to show real success in what is now "Obama's war" by the autumn of 2011 in order to get re-elected. He, at least, has something to hope for.

For Gordon Brown, though, there is little to gain but a lot to lose with the electorate from this phase of the war. If it goes badly he will be blamed but there will be little credit for success in an election campaign. The real beneficiary might be David Cameron, if the Conservatives win the election. In the event of victory, the Conservatives will announce a review of Britain's whole Afghan war strategy. This might just coincide in the late summer with real evidence of politico-military success in Helmand and Kandahar.

In Afghanistan itself, of course, this will be irrelevant. The eight wasted years of international involvement have been largely down to the political constraints western politicians put on a war that dared not speak its name until recently. At least we are starting to accept responsibility for what we have taken on.